Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor which indicates particulate matter mass and/or concentration in the exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels.
Particulate matter sensors may encounter problems with non-uniform deposition of soot on the sensor due to a bias in flow distribution across the surface of the sensor. Further, particulate matter sensors may be prone to contamination from an impingement of water droplets and/or larger particulates present in the exhaust gases. This contamination may lead to errors in sensor output. Furthermore, sensor regeneration may be inadequate when a substantial quantity of exhaust gases stream across the particulate matter sensor.
The inventors herein have recognized the above issues and identified an approach to at least partly address the issues. In one example approach, a system includes a tube with a plurality of gas intake apertures on an upstream surface, the tube having a horseshoe shape with a rounded notch on a downstream surface and a plurality of gas exit apertures positioned along a length of the rounded notch and a particulate matter sensor positioned inside the tube.
The system may further include a heat shield coupled to the particulate matter sensor at a first side of the heat shield, where a second side of the heat shield opposite the first side, faces the upstream surface of the tube. Thus, the heat shield may be positioned between the particulate matter sensor and the plurality of gas intake apertures to block the particulate matter sensor from exhaust gasses entering the tube. A bottom surface of the tube may include at least one drainage aperture, positioned proximate to the downstream surface of the tube for draining water droplets and particulates greater than a threshold size from the tube. In some examples, the particulate matter sensor may include an electrical circuit disposed on a first surface of the particulate matter sensor for measuring an amount of soot deposited on the electrical circuit, where the first surface faces the downstream surface of the tube. The plurality of gas exit apertures may be positioned along a length of the notch in a non-uniform arrangement, such that there are more apertures proximate to a bottom of the tube than a top of the tube.
In this way, a particulate matter sensor may be exposed to a more uniform flow distribution across its surface and water droplets and/or larger particulates may not reach the sensor element. As a result, the functioning of the particulate matter sensor may be improved and may be more reliable.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.